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Most Cited Journal of Hydrology Articles
The most cited articles published since 2010, extracted from Scopus.
A review of drought concepts
Volume 391, Issues 1-2, September 2010, Pages 202-216
Ashok K. Mishra | Vijay Pratap Singh,
Owing to the rise in water demand and looming climate change, recent years have witnessed much focus on
Journal of Hydrology
global drought scenarios. As a natural hazard, drought is best characterized by multiple climatological and
hydrological parameters. An understanding of the relationships between these two sets of parameters is
necessary to develop measures for mitigating the impacts of droughts. Beginning with a discussion of
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drought definitions, this paper attempts to provide a review of fundamental concepts of drought, classification
of droughts, drought indices, historical droughts using paleoclimatic studies, and the relation between
droughts and large scale climate indices. Conclusions are drawn where gaps exist and more research needs
to be focussed. © 2010 Elsevier B.V.
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Statistical bias correction of global simulated daily precipitation and temperature for the
application of hydrological models
Volume 395, Issues 3-4, December 2010, Pages 199-215
Claudio Piani | Graham P. Weedon | Martin J. Best | Sandra M. Gomes | Pedro A. Viterbo | Stefan
Hagemann | Jan O. Haerter
A statistical bias correction methodology for global climate simulations is developed and applied to daily land
precipitation and mean, minimum and maximum daily land temperatures. The bias correction is based on a
fitted histogram equalization function. This function is defined daily, as opposed to earlier published versions
in which they were derived yearly or seasonally at best, while conserving properties of robustness and
eliminating unrealistic jumps at seasonal or monthly transitions. The methodology is tested using the newly
available global dataset of observed hydrological forcing data of the last 50. years from the EU project
WATCH (WATer and global CHange) and an initial conditions ensemble of simulations performed with the
ECHAM5 global climate model for the same period. Bias corrections are derived from 1960 to 1969 observed
and simulated data and then applied to 1990-1999 simulations. Results confirm the effectiveness of the
methodology for all tested variables. Bias corrections are also derived using three other non-overlapping
decades from 1970 to 1999 and all members of the ECHAM5 initial conditions ensemble. A methodology is
proposed to use the resulting "ensemble of bias corrections" to quantify the error in simulated scenario
projections of components of the hydrological cycle. © 2010 Elsevier B.V.
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Beneath the surface of global change: Impacts of climate change on groundwater
Volume 405, Issues 3-4, August 2011, Pages 532-560
Timothy R. Green | Makoto Taniguchi | Henk Kooi | Jason J. Gurdak | Diana M. Allen | Kevin M. Hiscock |
Holger Treidel | Alice Aureli
Global change encompasses changes in the characteristics of inter-related climate variables in space and
time, and derived changes in terrestrial processes, including human activities that affect the environment. As
such, projected global change includes groundwater systems. Here, groundwater is defined as all subsurface
water including soil water, deeper vadose zone water, and unconfined and confined aquifer waters. Potential
effects of climate change combined with land and water management on surface waters have been studied
in some detail. Equivalent studies of groundwater systems have lagged behind these advances, but research
and broader interest in projected climate effects on groundwater have been accelerating in recent years. In
this paper, we provide an overview and synthesis of the key aspects of subsurface hydrology, including water
quantity and quality, related to global change.Adaptation to global change must include prudent management
of groundwater as a renewable, but slow-feedback resource in most cases. Groundwater storage is already
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Most Cited Journal of Hydrology Articles
over-tapped in many regions, yet available subsurface storage may be a key to meeting the combined
demands of agriculture, industry, municipal and domestic water supply, and ecosystems during times of
shortage. The future intensity and frequency of dry periods combined with warming trends need to be
addressed in the context of groundwater resources, even though projections in space and time are fraught
with uncertainty. Finally, potential impacts of groundwater on the global climate system are largely unknown.
Research to improve our understanding of the joint behaviors of climate and groundwater is needed, and
spin-off benefits on each discipline are likely. © 2011.
Global review and synthesis of trends in observed terrestrial near-surface wind speeds:
Implications for evaporation
Volume 416-417, Issue , January 2012, Pages 182-205
Tim R. McVicar | Michael L. Roderick | Randall J. Donohue | Lingtao Li | Thomas G. Van Niel | Axel G.
Thomas | Jürgen Grieser | Deepak Jhajharia | Youcef Himri | Natalie M. Mahowald | Anna V. Mescherskaya |
Andries C. Kruger | S. Rehman | Yagob Dinpashoh
In a globally warming climate, observed rates of atmospheric evaporative demand have declined over recent
decades. Several recent studies have shown that declining rates of evaporative demand are primarily
governed by trends in the aerodynamic component (primarily being the combination of the effects of wind
speed (u) and atmospheric humidity) and secondarily by changes in the radiative component. A number of
these studies also show that declining rates of observed near-surface u (termed 'stilling') is the primary factor
contributing to declining rates of evaporative demand. One objective of this paper was to review and
synthesise the literature to assess whether stilling is a globally widespread phenomenon. We analysed 148
studies reporting terrestrial u trends from across the globe (with uneven and incomplete spatial distribution
and differing periods of measurement) and found that the average trend was -0.014ms -1a -1 for studies with
more than 30 sites observing data for more than 30years, which confirmed that stilling was widespread.
Assuming a linear trend this constitutes a -0.7ms -1 change in u over 50years. A second objective was to
confirm the declining rates of evaporative demand by reviewing papers reporting trends in measured pan
evaporation (E pan) and estimated crop reference evapotranspiration (ET o); average trends were -3.19mma
-2 (n=55) and -1.31mma -2 (n=26), respectively. A third objective was to assess the contribution to
evaporative demand trends that the four primary meteorological variables (being u; atmospheric humidity;
radiation; and air temperature) made. The results from 36 studies highlighted the importance of u trends. We
also quantified the sensitivity of rates of evaporative demand to changes in u and how the relative
contributions of the aerodynamic and radiative components change seasonally over the globe. Our review: (i)
shows that terrestrial stilling is widespread across the globe; (ii) confirms declining rates of evaporative
demand; and (iii) highlights the contribution u has made to these declining evaporative rates. Hence we
advocate that assessing evaporative demand trends requires consideration of all four primary meteorological
variables (being u, atmospheric humidity, radiation and air temperature). This is particularly relevant for longterm water resource assessment because changes in u exert greater influence on energy-limited wateryielding catchments than water-limited ones. © 2011.
A copula-based joint deficit index for droughts
Volume 380, Issues 1-2, January 2010, Pages 121-134
Shihchieh Kao | Rao S. Govindaraju
Current drought information is based on indices that do not capture the joint behaviors of hydrologic
variables. To address this limitation, the potential of copulas in characterizing droughts from multiple variables
is explored in this study. Starting from the standardized index (SI) algorithm, a modified index accounting for
seasonality is proposed for precipitation and streamflow marginals. Utilizing Indiana stations with long-term
observations (a minimum of 80 years for precipitation and 50 years for streamflow), the dependence
structures of precipitation and streamflow marginals with various window sizes from 1- to 12-months are
constructed from empirical copulas. A joint deficit index (JDI) is defined by using the distribution function of
copulas. This index provides a probability-based description of the overall drought status. Not only is the
proposed JDI able to reflect both emerging and prolonged droughts in a timely manner, it also allows a
month-by-month drought assessment such that the required amount of precipitation for achieving normal
conditions in future can be computed. The use of JDI is generalizable to other hydrologic variables as
evidenced by similar drought severities gleaned from JDIs constructed separately from precipitation and
streamflow data. JDI further allows the construction of an inter-variable drought index, where the entire
dependence structure of precipitation and streamflow marginals is preserved. © 2009 Elsevier B.V. All rights
reserved.
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Assessing the ability of potential evaporation formulations to capture the dynamics in
evaporative demand within a changing climate
Volume 386, Issues 1-4, May 2010, Pages 186-197
Randall J. Donohue | Tim R. McVicar | Michael L. Roderick
Rates of evaporative demand can be modelled using one of numerous formulations of potential evaporation.
Physically, evaporative demand is driven by four key variables - net radiation, vapour pressure, wind speed,
and air temperature - each of which have been changing across the globe over the past few decades. In this
research we examine five formulations of potential evaporation, testing for how well each captures the
dynamics in evaporative demand. We generated daily potential evaporation datasets for Australia, spanning
1981-2006, using the: (i) Penman; (ii) Priestley-Taylor; (iii) Morton point; (iv) Morton areal; and (v)
Thornthwaite formulations. These represent a range in how many of the key driving variables are
incorporated within modelling. The testing of these formulations was done by analysing the annual and
seasonal trends in each against changes in precipitation (a proxy for actual evaporation), assuming that they
should vary in an approximately inverse manner. The four-variable Penman formulation produced the most
reasonable estimation of potential evaporation dynamics. An attribution analysis was performed using the
Penman formulation to quantify the contribution of each input variable to overall trends in potential
evaporation. Whilst changes in air temperature were found to produce a large increase in Penman potential
evaporation rates, changes in the other key variables each reduced rates, resulting in an overall negative
trend in Penman potential evaporation. This study highlights the need for spatially and temporally dynamic
data describing all drivers of evaporative demand, especially projections of each driving variable when
estimating the possible affects of climatic changes on evaporative demand. Crown Copyright © 2010.
Hospital effluents as a source of emerging pollutants: An overview of micropollutants and
sustainable treatment options
Volume 389, Issues 3-4, August 2010, Pages 416-428
P. Verlicchi | Alessio Galletti | Mira P. Petrović | Damià Barceló
Hospital wastewaters contain a variety of toxic or persistent substances such as pharmaceuticals,
radionuclides, solvents and disinfectants for medical purposes in a wide range of concentrations due to
laboratory and research activities or medicine excretion. Most of these compounds belong to the so called
emerging contaminants; quite often unregulated pollutants which may be candidates for future regulation
depending on research on their potential health effects and monitoring of their occurrence. Their main
characteristic is that they do not need to persist in the environment to cause negative effects since their high
transformation/removal rates can be compensated for by their continuous introduction into the
environment.Some of these compounds, most of them pharmaceuticals and personal care products may also
be present in urban wastewaters. Their concentrations in the effluents may vary from ngL-1 to μgL-1.In this
paper, hospital effluents and urban wastewaters are compared in terms of quali-quantitative characteristics.
On the basis of an in-depth survey: (i) hospital average specific daily water consumptions (L patient-1day-1)
are evaluated and compared to urban ones (L person-1day-1), (ii) conventional parameters concentrations in
hospital effluents are compared to urban ones and (iii) main pharmaceuticals and other emerging compounds
contents are compared in the two wastewaters. Finally, an overview of the removal capacity of the different
treatments is reported. © 2010 Elsevier B.V.
Quantifying blue and green virtual water contents in global crop production as well as
potential production losses without irrigation
Volume 384, Issues 3-4, April 2010, Pages 198-217
Stefan Siebert | Petra Döll
Crop production requires large amounts of green and blue water. We developed the new global crop water
model GCWM to compute consumptive water use (evapotranspiration) and virtual water content
(evapotranspiration per harvested biomass) of crops at a spatial resolution of 5′ by 5′, distinguishing 26 crop
classes, and blue versus green water. GCWM is based on the global land use data set MIRCA2000 that
provides monthly growing areas for 26 crop classes under rainfed and irrigated conditions for the period
1998-2002 and represents multi-cropping. By computing daily soil water balances, GCWM determines
evapotranspiration of blue and green water for each crop and grid cell. Cell-specific crop production under
both rainfed and irrigated conditions is computed by downscaling average crop yields reported for 402
national and sub-national statistical units, relating rainfed and irrigated crop yields reported in census
statistics to simulated ratios of actual to potential crop evapotranspiration for rainfed crops. By restricting
water use of irrigated crops to green water only, the potential production loss without any irrigation was
computed. For the period 1998-2002, the global value of total crop water use was 6685 km3 yr-1, of which
blue water use was 1180 km3 yr-1, green water use of irrigated crops was 919 km3 yr-1 and green water use
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of rainfed crops was 4586 km3 yr-1. Total crop water use was largest for rice (941 km3 yr-1), wheat (858
km3 yr-1) and maize (722 km3 yr-1). The largest amounts of blue water were used for rice (307 km3 yr-1)
and wheat (208 km3 yr-1). Blue water use as percentage of total crop water use was highest for date palms
(85%), cotton (39%), citrus fruits (33%), rice (33%) and sugar beets (32%), while for cassava, oil palm and
cocoa, almost no blue water was used. Average crop yield of irrigated cereals was 442 Mg km-2 while
average yield of rainfed cereals was only 266 Mg km-2. Average virtual water content of cereal crops was
1109 m3 Mg-1 of green water and 291 m3 Mg-1 of blue water, while average crop water productivity of cereal
crops was 714 g m-3. If currently irrigated crops were not irrigated, global production of dates, rice, cotton,
citrus and sugar cane would decrease by 60%, 39%, 38%, 32% and 31%, respectively. Forty-three per cent
of cereal production was on irrigated land, and without irrigation, cereal production on irrigated land would
decrease by 47%, corresponding to a 20% loss of total cereal production. The largest cereal production
losses would occur in Northern Africa (66%) and Southern Asia (45%) while losses would be very low for
Northern Europe (0.001%), Western Europe (1.2%), Eastern Europe (1.5%) and Middle Africa (1.6%).
Uncertainties and limitations are discussed in the manuscript, and a comparison of GCWM results to
statistics or results of other studies shows good agreement at the regional scale, but larger differences for
specific countries. © 2009 Elsevier B.V. All rights reserved.
A simple inertial formulation of the shallow water equations for efficient two-dimensional flood
inundation modelling
Volume 387, Issues 1-2, June 2010, Pages 33-45
Paul D. Bates | Matthew S. Horritt | Timothy J. Fewtrell
This paper describes the development of a new set of equations derived from 1D shallow water theory for
use in 2D storage cell inundation models where flows in the x and y Cartesian directions are decoupled. The
new equation set is designed to be solved explicitly at very low computational cost, and is here tested against
a suite of four test cases of increasing complexity. In each case the predicted water depths compare
favourably to analytical solutions or to simulation results from the diffusive storage cell code of Hunter et al.
(2005). For the most complex test involving the fine spatial resolution simulation of flow in a topographically
complex urban area the Root Mean Squared Difference between the new formulation and the model of
Hunter et al. is ~1cm. However, unlike diffusive storage cell codes where the stable time step scales with (1/
Δx)2, the new equation set developed here represents shallow water wave propagation and so the stability is
controlled by the Courant-Freidrichs-Lewy condition such that the stable time step instead scales with 1/Δx.
This allows use of a stable time step that is 1-3 orders of magnitude greater for typical cell sizes than that
possible with diffusive storage cell models and results in commensurate reductions in model run times. For
the tests reported in this paper the maximum speed up achieved over a diffusive storage cell model was
1120×, although the actual value seen will depend on model resolution and water surface gradient. Solutions
using the new equation set are shown to be grid-independent for the conditions considered and to have an
intuitively correct sensitivity to friction, however small instabilities and increased errors on predicted depth
were noted when Manning's n=0.01. The new equations are likely to find widespread application in many
types of flood inundation modelling and should provide a useful additional tool, alongside more established
model formulations, for a variety of flood risk management studies. © 2010 Elsevier B.V.
Characterisation of selected extreme flash floods in Europe and implications for flood risk
management
Volume 394, Issues 1-2, November 2010, Pages 118-133
Lorenzo Marchi | Marco Borga | Emanuele Preciso | Éric Gaume
High-resolution data enabling identification and analysis of the hydrometeorological causative processes of
flash floods have been collected and analysed for 25 extreme flash floods (60 drainage basins, ranging in
area from 9.5 to 1856km2) across Europe. Most of the selected floods are located in a geographical belt
crossing Europe from western Mediterranean (Catalunia and southwestern France) to Black Sea, covering
northern Italy, Slovenia, Austria, Slovakia and Romania. Criteria for flood selection were high intensity of
triggering rainfall and flood response and availability of high-resolution reliable data. Hydrometeorological
data collected and collated for each event were checked by using a hydrological model. The derivation and
analysis of summarising variables based on the data archive has made it possible to outline some
characteristics of flash floods in various morphoclimatic regions of Europe. Peak discharge data for more
than 50% of the studied watersheds derive from post-flood surveys in ungauged streams. This stresses both
the significance of post-flood surveys in building and extending flash flood data bases, and the need to
develop new methods for flash flood hazard assessment able to take into account data from post-event
analysis. Examination of data shows a peculiar seasonality effect on flash flood occurrence, with events in
the Mediterranean and Alpine-Mediterranean regions mostly occurring in autumn, whereas events in the
inland Continental region commonly occur in summer, revealing different climatic forcing. Consistently with
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this seasonality effect, spatial extent and duration of the events is generally smaller for the Continental events
with respect to those occurring in the Mediterranean region. Furthermore, the flash flood regime is generally
more intense in the Mediterranean Region than in the Continental areas. The runoff coefficients of the studied
flash floods are usually rather low (mean value: 0.35). Moderate differences in runoff coefficient are observed
between the studied climatic regions, with higher values in the Mediterranean region. Antecedent saturation
conditions have a significant impact on event runoff coefficients, showing the influence of initial soil moisture
status even on extreme flash flood events and stressing the importance of accounting soil moisture for
operational flash flood forecasting. The runoff response displays short lag times (mostly <6h). The identified
relations between watershed area, stream length and response time enable determination of a characteristic
mean velocity of the flash flood process (at basin scales less than 350km2), defined as the ratio of
characteristic length (mean river length) and time (response time or lag time), equal to 3ms-1. This is related
to the celerity with which the flood wave moves through the catchment. The analysis of the response time
provides information on the time resolution and the spatial density of the networks required for monitoring the
storms that generate flash floods. © 2010 Elsevier B.V.
Game theory and water resources
Volume 381, Issues 3-4, February 2010, Pages 225-238
Kaveh Madani
Managing water resources systems usually involves conflicts. Behaviors of stakeholders, who might be willing
to contribute to improvements and reach a win-win situation, sometimes result in worse conditions for all
parties. Game theory can identify and interpret the behaviors of parties to water resource problems and
describe how interactions of different parties who give priority to their own objectives, rather than system's
objective, result in a system's evolution. Outcomes predicted by game theory often differ from results
suggested by optimization methods which assume all parties are willing to act towards the best system-wide
outcome. This study reviews applicability of game theory to water resources management and conflict
resolution through a series of non-cooperative water resource games. The paper illustrates the dynamic
structure of water resource problems and the importance of considering the game's evolution path while
studying such problems. © 2009 Elsevier B.V. All rights reserved.
Estimation of seepage rates in a losing stream by means of fiber-optic high-resolution vertical
temperature profiling
Volume 380, Issues 1-2, January 2010, Pages 154-164
Tobias Vogt | Philipp Schneider | Lisa Hahn-Woernle | Olaf A. Cirpka
Vertical temperature profiling in the river beds of losing streams has been shown to be useful in obtaining
seepage rates. We present a method for high-resolution vertical temperature profiling in surface-water
sediments for detailed quantification of seepage flux over depth and time. The method is based on fiber-optic
distributed temperature sensing, in which temperature profiles along an optical fiber are obtained by making
use of Raman scattering. An optical fiber was wrapped around a 2 in. PVC tube and installed vertically within
the streambed sediment. The wrapping transfers the spatial resolution along the fiber of 1 m to a vertical
resolution of about 5 mm. The high-resolution temperature profiler was tested at a losing reach of the Swiss
prealpine River Thur resulting in a 20-day long temperature time series with a temporal resolution of 10 min.
The time series are analyzed by means of dynamic harmonic regression to obtain the diurnal contributions of
the measured time series at all depths and time points. The time for the diurnal temperature signal to reach
the observation depth and the associated attenuation of the signal are calculated from the phase angles and
amplitudes of the diurnal contributions. The time shift results in an apparent celerity of diurnal temperature
propagation, which is converted into an apparent seepage rate by fitting the data to the analytical solution for
convective-conductive heat transfer in a semi-infinite, uniform, one-dimensional domain with a sinusoidal
surface temperature. The high spatial resolution allows the location of discontinuities in the river bed which
would have remained undetected if temperature had been measured only at a few individual depths to be
identified. This is a particular strength of the fiber-optic high-resolution temperature profiler. The time series
also give evidence of sporadic high infiltration rates at times of high water tables. © 2009 Elsevier B.V. All
rights reserved.
Scenario-neutral approach to climate change impact studies: Application to flood risk
Volume 390, Issues 3-4, September 2010, Pages 198-209
Christel Prudhomme | Robert L. Wilby | Sue M. Crooks | Alison Kay | Nick S. Reynard
This paper presents a novel framework for undertaking climate change impact studies, which can be used for
testing the robustness of precautionary climate change allowances used in engineering design. It is illustrated
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with respect to fluvial flood risk in the UK. The methodology departs from conventional scenario-led impact
studies because it is based on sensitivity analyses of catchment responses to a plausible range of climate
changes (rather than the time-varying outcome of individual scenarios), making it scenario-neutral. The
method involves separating the climate change projections (the hazard) from the catchment responsiveness
(the vulnerability) expressed as changes in peak flows. By combining current understanding of likelihood of
the climate change hazard with knowledge of the sensitivity of a given catchment, it is possible to evaluate
the fraction of climate model projections that would not be accommodated by specified safety margins. This
enables rapid appraisal of existing or new precautionary allowances for a set of climate change projections,
but also for any new set of climate change projections for example arising from a new generation of climate
models as soon as they are available, or when focusing on a different planning time horizon, without the need
for undertaking a new climate change impact analysis with the new scenarios. The approach is demonstrated
via an assessment of the UK Government's 20% allowance for climate change applied in two contrasting
catchments. In these exemplars, the allowance defends against the majority of sampled climate projections
for the 2080s from the IPCC-AR4 GCM and UKCP09 RCM runs but it is still possible to identify a sub-set of
regional scenarios that would exceed the 20% threshold. © 2010 Elsevier B.V.
Wildfire effects on water quality in forest catchments: A review with implications for water
supply
Volume 396, Issues 1-2, January 2011, Pages 170-192
Hugh G. Smith | Gary J. Sheridan | Patrick N J Lane | Petter Nyman | Shane R. Haydon
Wildfires burn extensive forest areas around the world each year. In many locations, fire-prone forest
catchments are utilised for the supply of potable water to small communities up to large cities. Following
wildfire, increased erosion rates and changes to runoff generation and pollutant sources may greatly increase
fluxes of sediment, nutrients and other water quality constituents, potentially contaminating water supplies.
Most research to date has focused on suspended sediment exports and concentrations after wildfire.
Reported first year post-fire suspended sediment exports varied from 0.017 to 50tha-1year-1 across a large
range of catchment sizes (0.021-1655km2). This represented an estimated increase of 1-1459 times
unburned exports. Maximum reported concentrations of total suspended solids in streams for the first year
after fire ranged from 11 to 500,000mgL-1. Similarly, there was a large range in first year post-fire stream
exports of total N (1.1-27kgha-1year-1) and total P (0.03-3.2kgha-1year-1), representing a multiple change of
0.3-431 times unburned, while NO3- exports of 0.04-13.0kgha-1year-1 (3-250 times unburned) have been
reported. NO3-, NO2-, and NH3/NH4+ concentrations in streams and lakes or reservoirs may increase after
wildfire but appear to present a generally low risk of exceeding drinking water guidelines. Few studies have
examined post-fire exports of trace elements. The limited observations of trace element concentrations in
streams after wildfire found high levels (well over guidelines) of Fe, Mn, As, Cr, Al, Ba, and Pb, which were
associated with highly elevated sediment concentrations. In contrast, Cu, Zn, and Hg were below or only
slightly above guideline values. Elevated Na+, Cl- and SO42- solute yields have been recorded soon after
fire, while reports of concentrations of these constituents were mostly confined to coniferous forest areas in
North America, where maximum sampled values were well below recommended limits. Likewise, reported
wildfire effects on dissolved organic carbon were generally minor and elevated concentrations largely
reflected background conditions. Available cyanide concentrations in small streams may approach levels of
concern soon after fire, but increases are likely to be of short duration. Post-fire concentrations of polycyclic
aromatic hydrocarbons in streams have been found to increase but remained within the recommended limit.
Large increases in exports and concentrations of some constituents after wildfire indicate the potential for
impacts on water supply from forest catchments. In response, various water treatment measures may be
required and in the absence of adequate treatment facilities or alternative sources, water supplies may be
vulnerable to disruption. © 2010 Elsevier B.V.
Trends in reference crop evapotranspiration over Iran
Volume 399, Issues 3-4, March 2011, Pages 422-433
Yagob Dinpashoh | Deepak Jhajharia | Ahmad Fakheri Fard | Vijay Pratap Singh, | Ercan Kahya
This study examined the trends in reference crop evapotranspiration (ET0) on monthly and annual time
scales in Iran. ET0 was estimated using the globally accepted Food and Agriculture Organization (FAO)
Penman Monteith method (FAO-56 PM) over the 16 weather stations located in the different regions of Iran.
The trends in ET0 were detected by using the Mann-Kendall (MK) test after the removal of the significant lag1 serial correlation effect from all the ET0 time series by pre-whitening. The slopes of trend lines were
computed using the Theil-Sen's slope estimator. The spatial and temporal homogeneity of trends were tested
as well. The multiple regression analysis was performed in each time series of the governing meteorological
variables to identify the cause of observed trends in ET0. Results showed that both statistically significant
increasing and decreasing trends were observed in the annual and monthly ET0. The increasing trends in
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ET0 were more pronounced than the decreasing trends. In annual time scale, the strong positive (negative)
trend in ET0 over Iran of the magnitude of about 186 (-65) mm/year per decade was observed. In monthly
time scale there was greater number of increasing trends than that of the decreasing trends in most of the
warm months. The most strong positive (negative) trend magnitude was found in April (July) with Theil-Sen's
slope equal to 14 (-8.7) mm/year per decade. The results of homogeneity test indicated no homogeneity in
ET0 trends between the stations and months when the entire study domain is considered. Wind speed was
found to be the most dominant variable influencing ET0 in all the months except the winter months in Iran. ©
2011 Elsevier B.V.
Uncertainty of downscaling method in quantifying the impact of climate change on hydrology
Volume 401, Issues 3-4, May 2011, Pages 190-202
Jie Chen | François P. Brissette | Robert Leconte
Uncertainty estimation of climate change impacts has been given a lot of attention in the recent literature. It is
generally assumed that the major sources of uncertainty are linked to General Circulation Models (GCMs)
and Greenhouse Gases Emissions Scenarios (GGES). However, other sources of uncertainty such as the
choice of a downscaling method have been given less attention. This paper focuses on this issue by
comparing six downscaling methods to investigate the uncertainties in quantifying the impacts of climate
change on the hydrology of a Canadian (Quebec province) river basin. The downscaling methods regroup
dynamical and statistical approaches, including the change factor method and a weather generator-based
approach. Future (2070-2099, 2085 horizon) hydrological regimes simulated with a hydrological model are
compared to the reference period (1970-1999) using the average hydrograph, annual mean discharge, peak
discharge and time to peak discharge as criteria. The results show that all downscaling methods suggest
temperature increases over the basin for the 2085 horizon. The regression-based statistical methods predict
a larger increase in autumn and winter temperatures. Predicted changes in precipitation are not as
unequivocal as those of temperatures, they vary depending on the downscaling methods and seasons. There
is a general increase in winter discharge (November-April) while decreases in summer discharge are
predicted by most methods. Consistently with the large predicted increases in autumn and winter
temperature, regression-based statistical methods show severe increases in winter flows and considerable
reductions in peak discharge. Across all variables, a large uncertainty envelope was found to be associated
with the choice of a downscaling method. This envelope was compared to the envelope originating from the
choice of 28 climate change projections from a combination of seven GCMs and three GGES. Both
uncertainty envelopes were similar, although the latter was slightly larger. The regression-based statistical
downscaling methods contributed significantly to the uncertainty envelope. Overall, results indicate that
climate change impact studies based on only one downscaling method should be interpreted with caution. ©
2011 Elsevier B.V.
Parameter and modeling uncertainty simulated by GLUE and a formal Bayesian method for a
conceptual hydrological model
Volume 383, Issues 3-4, March 2010, Pages 147-155
Xiaoli Jin | Chongyu Xu | Qi Zhang | Vijay Pratap Singh,
Quantification of uncertainty of hydrological models has attracted much attention in hydrologic research in
recent years. Many methods for quantification of uncertainty have been reported in the literature, of which
GLUE and formal Bayesian method are the two most popular methods. There have been many discussions
in the literature concerning differences between these two methods in theory (mathematics) and results, and
this paper focuses on the computational efficiency and differences in their results, but not on philosophies and
mathematical rigor that both methods rely on. By assessing parameter and modeling uncertainty of a simple
conceptual water balance model (WASMOD) with the use of GLUE and formal Bayesian method, the paper
evaluates differences in the results of the two methods and discusses the reasons for these differences. The
main findings of the study are that: (1) the parameter posterior distributions generated by the Bayesian
method are slightly less scattered than those by the GLUE method; (2) using a higher threshold value (>0.8)
GLUE results in very similar estimates of parameter and model uncertainty as does the Bayesian method;
and (3) GLUE is sensitive to the threshold value used to select behavioral parameter sets and lower
threshold values resulting in a wider uncertainty interval of the posterior distribution of parameters, and a
wider confidence interval of model uncertainty. More study is needed to generalize the findings of the present
study. © 2010 Elsevier B.V.
Climate non-stationarity - Validity of calibrated rainfall-runoff models for use in climate
change studies
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Volume 394, Issues 3-4, November 2010, Pages 447-457
Jai Vaze | David A. Post | Francis Chiew | Jean Michel Perraud | Neil R. Viney | Jin Teng
This paper presents results from a modelling study carried out to investigate whether the calibrated parameter
values for rainfall-runoff models based on historical observed data can be used to reliably predict runoff
responses to changes in future climate inputs. The modelling experiments are carried out for four rainfallrunoff models using long records of historical daily climate and streamflow data from 61 catchments in
southeast Australia. The results indicate that the models, when calibrated using more than 20. years of data,
can generally be used for climate impact studies where the future mean annual rainfall is not more than 15%
drier or 20% wetter than the mean annual rainfall in the model calibration period. It is generally more difficult
for a model calibrated over a wet period to predict runoff over a dry period compared to a model calibrated
over a dry period to predict runoff over a wet period. For southeast Australia, there is a good reason to use
the recent records to calibrate rainfall-runoff models to represent the current prolonged drought over the
region and for climate change impact studies where the large majority of climate models predict a drier future
across this region. © 2010 Elsevier B.V.
Hydraulic parameter estimation by remotely-sensed top soil moisture observations with the
particle filter
Volume 399, Issues 3-4, March 2011, Pages 410-421
Carsten Montzka | Hamid Moradkhani | Lutz Weihermüller | H. J. Hendricks Franssen | Morton John Canty |
Harry Vereecken
In a synthetic study we explore the potential of using surface soil moisture measurements obtained from
different satellite platforms to retrieve soil moisture profiles and soil hydraulic properties using a sequential
data assimilation procedure and a 1D mechanistic soil water model. Four different homogeneous soil types
were investigated including loamy sand, loam, silt, and clayey soils. The forcing data including precipitation
and potential evapotranspiration were taken from the meteorological station of Aachen (Germany). With the
aid of the forward model run, a synthetic data set was designed and observations were generated. The
virtual top soil moisture observations were then assimilated to update the states and hydraulic parameters of
the model by means of a particle filtering data assimilation method. Our analyses include the effect of
assimilation strategy, measurement frequency, accuracy in surface soil moisture measurements, and soils
differing in textural and hydraulic properties. With this approach we were able to assess the value of periodic
spaceborne observations of top soil moisture for soil moisture profile estimation and identify the adequate
conditions (e.g. temporal resolution and measurement accuracy) for remotely sensed soil moisture data
assimilation. Updating of both hydraulic parameters and state variables allowed better predictions of top soil
moisture contents as compared with updating of states only. An important conclusion is that the assimilation
of remotely-sensed top soil moisture for soil hydraulic parameter estimation generates a bias depending on
the soil type. Results indicate that the ability of a data assimilation system to correct the soil moisture state
and estimate hydraulic parameters is driven by the non linearity between soil moisture and pressure head. ©
2011 Elsevier B.V.
Comparison of three downscaling methods in simulating the impact of climate change on the
hydrology of Mediterranean basins
Volume 383, Issues 1-2, March 2010, Pages 111-124
Pere Quintana-Seguí | Aur Ribes | Éric S. Martin | Florence Habets | Julien Boé
Studies of the impact of climate change on water resources usually follow a top to bottom approach: a
scenario of emissions is used to run a GCM simulation, which is downscaled (RCM and/or stastistical
methods) and bias-corrected. Then, this data is used to force a hydrological model. Seldom, impact studies
take into account all relevant uncertainties. In fact, many published studies only use one climate model and
one downscaling technique. In this study, the outputs of an atmosphere-ocean regional climate model are
downscaled and bias-corrected using three different techniques: a statistical method based on weather
regimes, a quantile-mapping method and the method of the anomaly. The resulting data are used to force a
distributed hydrological model to simulate the French Mediterranean basins. These are characterized by
water scarcity and an increasing human pressure, which cause a demand in assessments on the impact of
climate change hydrological systems. The purpose of the study is mainly methodological: the evaluation of
the uncertainty related to the downscaling and bias-correction step. The periods chosen to compare the
changes are the end of the 20th century (1970-2000) and the middle of the 21st century (2035-2065). The
study shows that the three methods produce similar anomalies of the mean annual precipitation, but there
are important differences, mainly in terms of spatial patterns. The study also shows that there are important
differences in the anomalies of temperature. These uncertainties are amplified by the hydrological model. In
some basins, the simulations do not agree in the sign of the anomalies and, in many others, the differences in
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amplitude of the anomaly are very important. Therefore, the uncertainty related to the downscaling and biascorrection of the climate simulation must be taken into account in order to better estimate the impact of
climate change, with its uncertainty, on a specific basin. The study also shows that according to the RCM
simulation used and to the periods studied, there might be significant increases of winter precipitation on the
Cévennes region of the Massif Central, which is already affected by flash floods, and significant decreases of
summer precipitation in most of the region. This will cause a decrease in the average discharge in the middle
of the 21st in most of the gauging stations studied, specially in summer. Winter and, maybe spring, in some
areas, are the exception, as discharge may increase in some basins. © 2009 Elsevier B.V. All rights reserved.
Event soil loss, runoff and the Universal Soil Loss Equation family of models: A review
Volume 385, Issues 1-4, May 2010, Pages 384-397
Peter Ian Alexander Kinnell
The Universal Soil Loss Equation (USLE) is the most widely used and misused prediction equation in the
world. Although it was designed to predict long-term average annual soil loss, it has the capacity to predict
event soil losses reasonably well at some geographic locations and not well at others. Its lack of capacity to
predict event erosion is highly influenced by the fact the event rainfall-runoff factor used in the USLE and its
revisions (RUSLE, RUSLE2) does not consider runoff explicitly. While including direct consideration of runoff
in the event rainfall-runoff factor improves the capacity to predict event erosion when runoff is measured, that
capacity is reduced by inaccurate runoff prediction methods. Even so, the predictions may be better than
when the traditional event rainfall-runoff factor is used if the rainfall-runoff model used to predict runoff works
reasonably well. Direct consideration of runoff in the rainfall-runoff factor may improve the ability of the model
to account for seasonal effects. It also enhances the ability of the model to account for the spatial variations
in soil loss on hillslopes which result from spatial variations in soil and vegetation. However, the USLE model
will not provide a capacity to account for deposition taking place on concave hillslopes unless it is coupled
with an appropriate sediment transport model, as in done in RUSLE2. Changing the basis of the event
rainfall-runoff factor has consequences on a number of the other factors used in the model, in particular new
values of the soil erodibility factor need to be determined. Using runoff values from cropped areas is
necessary to account for differences in infiltration capacities between vegetated and tilled bare fallow areas,
but requires re-evaluation of the crop factors. © 2010 Elsevier B.V. All rights reserved.
Development of a coupled wavelet transform and neural network method for flow forecasting
of non-perennial rivers in semi-arid watersheds
Volume 390, Issues 1-2, August 2010, Pages 85-91
Jan Franklin Adamowski | Karen Sun
In this study, a method based on coupling discrete wavelet transforms (WA) and artificial neural networks
(ANN) for flow forecasting applications in non-perennial rivers in semi-arid watersheds is proposed. The
discrete à trous wavelet transform is used to decompose flow time series data into wavelet coefficients. The
wavelet coefficients are then used as inputs into Levenberg Marquardt artificial neural network models to
forecast flow. The relative performance of the coupled wavelet-neural network models (WA-ANN) was
compared to regular artificial neural network (ANN) models for flow forecasting at lead times of 1 and 3. days
for two different rivers in Cyprus (Kargotis at Evrychou and Xeros at Lazarides). In both cases, the coupled
wavelet-neural network models were found to provide more accurate flow forecasts than the artificial neural
network models. The results indicate that coupled wavelet-neural network models are a promising new
method of short-term flow forecasting in non-perennial rivers in semi-arid watersheds such as those found in
Cyprus. © 2010 Elsevier B.V.
First determination of C60 and C70 fullerenes and N-methylfulleropyrrolidine C60 on the
suspended material of wastewater effluents by liquid chromatography hybrid quadrupole
linear ion trap tandem mass spectrometry
Volume 383, Issues 1-2, March 2010, Pages 44-51
Marinella La Farré | Sandra Perez | Krisztina Gajda-Schrantz | Victoria Osorio | Lina Kantiani | Antoni
The increasing use and production of carbon-based nanoparticles demands for new analytical approaches
able to achieve sensitivities in the low ng/L range in order to assess their presence in environmental
samples. This paper describes development, optimization and validation of a novel method for the analysis of
C60 and, C70 fullerenes and N-methylfulleropyrrolidine C60 in the environment. The method relies on
ultrasonication extraction from suspended solids in wastewater, followed by liquid chromatography (LC)
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coupled to a hybrid triple quadrupole linear ion trap mass spectrometry (QqLIT-MS) for trace quantification.
Recoveries obtained were generally higher than 60% for both surface water and wastewaters. The overall
variability of the method was below 15%, for the three fullerenes and all tested matrices: ultra-pure water,
surface water and wastewater. For the effluents of wastewater treatment plants the method quantification
limits (MQL) ranged from 0.2 to 1 ng/L. The precision of the method, calculated as relative standard deviation
(RSD), ranged from 1% to 2% and from 5% to 9% for intra and inter-day analysis, respectively. The
developed analytical method was applied to the analysis of fullerenes in the effluents of 22 wastewater
treatment plants in Catalonia (NE of Spain). 50% of the analyzed samples contained fullerenes, nine of them
in the μg/L concentration range. This work constitutes the first report on the occurrence of fullerenes in
suspended solids of wastewater effluents highlighting the need of nanotechnologies residues assessment for
risk evaluation of nanoparticles in the environment. © 2009 Elsevier B.V. All rights reserved.
An estimation of global virtual water flow and sources of water withdrawal for major crops
and livestock products using a global hydrological model
Volume 384, Issues 3-4, April 2010, Pages 232-244
Naota Hanasaki | Toshiyuki Inuzuka | Shinjiro Kanae | Taikan Oki
The concept of virtual water, which is the volume of water consumption required to produce commodities
traded to an importing or exporting nation (or any region, company, individual, etc.), is a useful complement
to water resource analyses of water availability and use by region. Identifying the source of virtual water,
such as precipitation (green water) and irrigation water (blue water), further enhances this concept because
each differs in the level of sustainability and opportunity cost. Recent improvements in global hydrological
models consisting of both physically based hydrological and anthropogenic activity modules enabled us to
simulate the virtual water content of major crops consistent with their global hydrological simulation.
Enhancing one of these models, called H08, we were able to assess two major sources of virtual water flow
or content simultaneously: green water and blue water. Blue water was further subdivided into three
subcategories (i.e., streamflow, medium-size reservoirs, and nonrenewable and nonlocal blue water). We
conducted a global hydrological simulation for 15 years from 1985 to 1999 at a spatial resolution of 0.5° ×
0.5° (longitude and latitude). Total precipitation on land was 113,900 km3 yr-1, with 72,080 km3 yr-1 on
average evaporating in the period 1985-1999. Green water evapotranspiration from rainfed and irrigated
cropland and blue water evapotranspiration from irrigated cropland was estimated at 7820, 1720, and 1530
km3 yr-1, respectively. Next, using global trade data for 2000 and the simulated virtual water content of major
crops, the virtual water flow was estimated globally. Our results indicated that the global virtual water export
(i.e., the volume of water that an exporting nation consumes to produce the commodities that it trades
abroad) of five crops (barley, maize, rice, soybean, and wheat) and three livestock products (beef, pork, and
chicken) is 545 km3 yr-1. Of the total virtual water exports, 61 km3 yr-1 (11%) are blue water (i.e., irrigation
water) and 26 km3 yr-1 (5%) are nonrenewable and nonlocal blue water. © 2009 Elsevier B.V. All rights
reserved.
Bias correction of regional climate model simulations for hydrological climate-change impact
studies: Review and evaluation of different methods
Volume 456-457, Issue , August 2012, Pages 12-29
Claudia Teutschbein | Jan Seibert
Despite the increasing use of regional climate model (RCM) simulations in hydrological climate-change
impact studies, their application is challenging due to the risk of considerable biases. To deal with these
biases, several bias correction methods have been developed recently, ranging from simple scaling to rather
sophisticated approaches. This paper provides a review of available bias correction methods and
demonstrates how they can be used to correct for deviations in an ensemble of 11 different RCM-simulated
temperature and precipitation series. The performance of all methods was assessed in several ways: At first,
differently corrected RCM data was compared to observed climate data. The second evaluation was based
on the combined influence of corrected RCM-simulated temperature and precipitation on hydrological
simulations of monthly mean streamflow as well as spring and autumn flood peaks for five catchments in
Sweden under current (1961-1990) climate conditions. Finally, the impact on hydrological simulations based
on projected future (2021-2050) climate conditions was compared for the different bias correction methods.
Improvement of uncorrected RCM climate variables was achieved with all bias correction approaches. While
all methods were able to correct the mean values, there were clear differences in their ability to correct other
statistical properties such as standard deviation or percentiles. Simulated streamflow characteristics were
sensitive to the quality of driving input data: Simulations driven with bias-corrected RCM variables fitted
observed values better than simulations forced with uncorrected RCM climate variables and had more narrow
variability bounds. © 2012 Elsevier B.V.
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